This invention relates to a tower crane which comprises a pylon and a telescopic jib with travelling crab mounted thereon, which jib comprises at least two slidable jib parts, namely a foot part fastened to said pylon and a slidable point part, which parts each have a runway extending along the lengthwise direction thereof for the travelling crab, which jib has means to lock both said jib parts relative to one another, which crane is provided with a winch and a cable made fast thereto for sliding said jib in and out as well as for traversing said travelling crab over the jib, a first cable portion which can move the crab away from said pylon, being made fast to said travelling crab and running over at least one cable pulley mounted on that end removed from the pylon of the jib point part to the winch, and a second cable portion which can move said crab towards the pylon, also being made fast to said travelling crab and running over ar least one cable pulley mounted on that end lying on the pylon side of the jib foot part to the winch, whereby both cable portions are so wound on the winch drum that as the one portion is wound on said drum, the other portion is unwound therefrom.
In known tower cranes of this kind, the first cable portion runs from that cable pulley on that point part end removed from the pylon, towards said pylon up to a cable pulley which is mounted on that point part end facing the pylon, then back away from the pylon and about a cable pulley which is mounted on that end removed from said pylon, of the jib foot part. Said first cable portion runs finally up to the pylon, either directly to said winch when same is mounted on the jib foot part, or over a cable pulley mounted on said foot part against said pylon, to the lower side of said pylon or the stand which bears said pylon, when the winch is mounted thereon. The second cable portion runs from the travelling crab directly to that end lying on the pylon side, of the jib foot part and is made fast there to said winch when same is mounted on said foot part, or runs there over a pulley mounted on said foot part to the lower side of the tower crane when said winch is is mounted at the bottom of said crane.
In such known cranes, the first cable portion can move said travelling crab away from the pylon while the jib is retracted and the jib parts are connected together. Once the travelling crab has reached that end removed from the pylon, of the jib foot part, the jib parts are uncoupled from one another, while the travelling crab is automatically coupled to the jib point part. By means of said first cable portion, the jib may now be extended, whereby the travelling crab thus moves together with the jib point portion. To retract the jib again, the travelling crab has first to be locked again on the free end of the jib point part. By means of the second cable portion the travelling crab is pulled towards the pylon whereby thus the jib point part retracts into the foot part. When said point part is completely retracted, the jib parts are automatically locked together, but the travelling crab is automatically released from the point part, in such a way that said travelling crab can now be moved over the jib foot part by means of the second cable portion. In the extended position of the jib, the travelling crab after being uncoupled from the point part, can be moved but only over said point part.
Due to the devices required for coupling and uncoupling the travelling crab relative to said jib point part, besides the already required device for coupling together the jib parts, such known tower cranes are quite expensive. Moreover the use of such a tower crane is not very flexible as the load cannot be moved over the whole length of the extended jib without sliding in and out said jib according to the movement direction of said load.
The invention has now for object to obviate the above drawbacks and provide a tower crane which comprises a pylon and a telescopic jib mounted thereon with a travelling crab, whereby said crab can move in a very simple way, both with a completely extended jib and with a completely retracted jib, as well as in various intermediate positions of said jib, over the whole jib length without having to slide in or out said jib, while neither for the sliding out nor for the sliding in of the jib, intricate locking mechanisms are required for locking the travelling crab.